1. Field of the Invention
The present invention relates to a minute capacitance element with a minute capacitance and, more specifically, to a large scale integrated circuit semiconductor device (LSI) using the minute capacitance element to be usable for a digital/analog (D/A) conversion, analog/digital (A/D) conversion or the like.
2. Description of the Related Art
In recent years, there is a demand for a High Definition liquid crystal display (HDLCD) as a display device with 1,920×1,080 pixels or more. As to the HDLCD, there is also a demand for a gray scale displaying or the like of a high gray scale e.g., colors of thousand millions higher than a conventional 8-bit gray scale. Therefore it is requested that a HDLCD driver of semiconductor device for driving the HDLCD is advanced of functional performance.
The HDLCD driver is required to have a D/A conversion circuit with a high-speed and high-performance capable of a multi-bit processing, since digital video signals input thereto are subject to the D/A conversion.
The D/A conversion circuit mainly comprises an amplifier circuit and a resistive DAC (i.e., resister type Digital to Analog Converter using an array of the resistance elements) or capacitive DAC (i.e., capacitor type Digital to Analog Converter using an array of the capacitance elements) or combination thereof. In the D/A conversion circuit, the resistive DAC or capacitive DAC mainly determines an accuracy of output and a device size. It is important how to control an area of the resistive DAC or capacitance DAC to be small, while keeping the accuracy of output of the D/A conversion circuit. In addition, there are many problems in cross-over capacitances, dielectric materials or the like for the circuit designing since those components are made densely as thin film resistance elements, so that the interlayer circuit designing is complicated frequently. Thus, the capacitive DAC is used widely.
The designing and formation of a high accuracy D/A conversion circuit are requested in order to manufacture HDLCD driver LSIs. Thus the array of the capacitance elements is provided for adjustment of the capacitive DAC. Further, a capacitance element having a capacitance value of from several tens atto-farads to several femto-farads is called as a minute capacitance element hereinafter, but the capacitance of the minute capacitance element is not limited to such a capacitance value.
Whereas, there is known conventionally an interdigital capacitor as a capacitance element of the capacitive DAC (See Japanese Patent Application Publication No. 5-235381) so that two comb-like conductor electrodes are formed on the same insulator film in such a manner that respective electrode fingers of the both electrodes are alternately arranged The interdigital capacitor is suitable for formation of the capacitance element having several tens atto-farads to several femto-farads with a high accuracy formed on the same insulator film.
Furthermore, there is a propose configuration for a capacitance element with a small capacitance value, as shown in FIGS. 1A and 1B, which comprises the first and second metal conductors connected respectively to the first and second metal wirings on the insulator film over the semiconductor substrate characterized in that the first and second metal conductors have leading ends B facing each other to be a capacitor with a wide width thereof (See Japanese Patent Application Publication No. 2006-237127). Further, FIG. 1A shows a schematic partial plane view of the capacitance element and, FIG. 1B shows a cross-section view taken along a broken line endpoint arrow line of FIG. 1A.
In the conventional minute capacitance element, as shown in FIG. 2, there exist fringing capacitances (broken lines) between the edges of the opposite facets of leading ends B other than the opposite facets of rectangular leading ends B facing each other of the first and second metal conductors. The fringing capacitances exert an influence on the increase of capacitance as a problem.
In addition, as shown in FIG. 3, the conventional minute capacitance element may have electrodes whose the leading ends B are rounded and dependent on the finishing of process although to be a rectangle shape, so that the capacitance value thereof is apt to be inconstant as a problem.
In other words, the conventional minute capacitance element has a problem that the fringing capacitances about the opposite facets of the metal conductors and the evenness of the leading ends' shape exert an influence on the capacitance of the device.